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<h1>Major Objects in WebCore</h1>
<div>Adam Barth</div>
<div>first draft, 2009-08-12</div>

<p>WebCore uses a number of objects to represent a web page in memory.  This
document describes the major objects and the relation between them.  In some
cases, the connection between these objects can be broken, resulting in null
pointers.  When traversing these pointers, code must be careful to consider
the "detached" case and gracefully handle null pointers.</p>

<pre class="asciiart">
 +---------+
 | Chrome  |
 +----+----+
      |
  +---+---+     +----------+
  | Page  +---->| Settings |
  +---+---+     +----------+
      |
      +-------------------------- ... other Frame objects
      |
  +---+---+   +-------------+                 +-------------------+
  | Frame +---+ FrameLoader +                 | JSDOMWindowShell  |
  +---+---+   +-------------+                 +---------+---------+
     / \                                                |
    /   \      /\  Re-used after navigation   /\        |
.../....|...............................................|..........
  /     |      \/  Replaced after navigation  \/        |
 /      |                                               |
/&lt;------|&lt;-- Ptrs to Frame are null after navigation[1] |
|       |                                               |
| +-----+-----+         +-------------+                 |
| | DOMWindow |&lt;--impl--+ JSDOMWindow |&lt;------window----+
| +-----+-----+         +-------------+
|       |
|       |&lt;-- Can be null for Documents created by XMLHttpRequest
|       |
| +-----+-----+         +-------------+
+-+ Document  |&lt;--impl--+ JSDocument  |
  +-----+-----+         +-------------+
        |
        |&lt;-- Can be null for DocumentType objects
        |
    +---+---+           +--------+
    | Node  |&lt;---impl---| JSNode |
    +-------+           +--------+
</pre>

<p>[1] After navigating to a new page, the old DOMWindow and old Document point
to a null Frame, and the Frame points to a new DOMWindow and a new Document.</p>

<p>If you have any comments on the above or other ideas about improving the clarity,
scope, or presentation, please send mail to the <a href="/contact.html">WebKit
mailing list</a>.</p>

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